The importance of proper air filtration equipment has received increased recognition over the last few years. Increasingly, consumers are opting for air filters which have a greater efficiency in removing undesirable matter from the air. The desire for better air filters extends to both the home and workplace.
One problem with the purchase of a proper air filter is the wide range of sizes which must be supported for various residential and commercial air conditioning and heating equipment. While a number of standard sizes exist, the number of different sizes which must be carried by a supplier is great. Unusual sizes, therefore, may be hard to find. Further, a consumer may not know the appropriate filter size when he or she is in a position to make a purchase, such as when the consumer is at a hardware store.
Accordingly, a number of filter kits have been developed that let the consumer (who may be a homeowner or a contractor, for example) assemble an air filter according to his or her needs, without prior knowledge of the correct size. This allows the supplier or contractor to carry a single kit which covers a wide range of filter sizes.
Present day adjustable filter kits have significant drawbacks, particularly in ease of assembly. In many cases the consumer must perform a significant amount of work in measuring and cutting the parts of the kit. Further, many present day kits are limited in size range, and therefore do not cover all popular air filter sizes. Available adjustable filters also provide inadequate sealing with the filter holding device in which they are mounted, thereby allowing significant amounts of air to pass by the filter.
One example of a present day adjustable air filtration kit 10 is shown in FIG. 1a. This kit comprises filtering material 12 (shown in the cutaway view) which is held between mesh 14 in frame 16. Frame 16 is comprised of four corner pieces, denoted generally by reference numeral 18, including two male (outer) corner pieces 18a and two female (inner) corner pieces 18b which are slideably engaged to effect a frame of the proper size.
This type of filter kit has three distinct problems. First, the design of the filter uses male corner pieces, which are dimensioned to slide within the female pieces. Thus, a relatively large portion of the frame will not seal properly with the filter holding device, which is expecting a frame of uniform thickness. Consequently, air is allowed to bypass the filter in these areas.
Second, a fairly fine mesh is generally used to simplify cutting of the mesh material to a desired size. A fine mesh, however, significantly increases the air flow resistance of the air filter. The use of a wider mesh is inconvenient because cutting the mesh will often result in exposed barbs 22 (see FIG. 1b) which make the final assembly more difficult.
Third, although the manufacturer of the kit may provide a template, such as described in connection with U.S. Pat. No. 5,087,276 to Snyder, actual assembly of the frame and cutting of the mesh and filter medium is typically cumbersome.
One method of improving the efficiency of an air filter is to apply a voltage to the filter to increase the filtering efficiency of the filtering elements within the filter. This method is discussed in U.S. Pat. No. 4,549,887. Filters employing an electric field have two distinct problems: (1) The bulk of the power supply greatly diminishes the filtering area of the filter and (2) the application of a high voltage from an external power source is cumbersome and potentially dangerous.
Therefore, a need has arisen in the industry for an adjustable air filter kit which is capable of accommodating a wide range of filter sizes, and which is easily sized, and further, a filter which can accommodate an electric field without significantly affecting filter size or requiring a high voltage external power supply.